1. Field of the Invention
This invention relates to apparatus for producing wire conductors for cables, and in particular to improved heat treating apparatus for such wire conductors.
2. Description of the Prior Art
In the manufacture of plastics coated telephone cable the metallic conductor wires are normally drawn, and then annealed, before being coated with plastics insulation. Sometimes these three processes are carried out entirely separately and independently of each other, but a preferred method of manufacture involves a tandem arrangement of the drawing and annealing process stages, or alternatively a tandem arrangement of all three stages, so that there is an uninterrupted flow of wire through the stages that are arranged in tandem.
For tandem operation an annealing method is required which will operate in a continuous mode of operation on the wire as it emerges at line speed from the drawing process. A common method of on-line annealing involves passing a large electrical current through the wire as it moves on between a system of two or more electrically conductive contact pulleys, which are connected to a current source, and so act as rolling contacts. Using this annealing method with the known type of phosphor-bronze pulleys, or alternatively, pulleys with tyres or contact faces of phosphor-bronze, copper wire is easily produced in an annealed condition suitable for further processing into telephone cables. In order to minimize wire breakage the contact pulleys are driven at a rate providing a small amount of slip ensuring that the peripheral speed of the pulleys is never allowed to be exceeded by the line speed of the wire passing over them. The slip is prone to produce sparking at points of contact, but in practice causes minimal damage, and the wear on the contact pulleys, although significant, can be tolerated. If however the same apparatus is used to anneal wire of other materials, such as aluminum, much less satisfactory results are produced. In particular there is excessive wear of the contact pulleys and sparking which results in a poor surface finish and a much higher incidence of wire breaks. The known apparatus also generally uses driven guide pulleys which may result in excessive tension in the wire. The use of free-running electrical contact pulleys for wire annealing is also known, such as shown in U.S. Pat. No. 2,109,555 issued Nov. 5, 1935. These provide some reduction of the wire tension, but still further reductions are desirable.